Video decoding apparatus and method

ABSTRACT

A video decoding apparatus and method capable of performing high-speed reproduction of image data subjected to coding with a prescribed coding scheme for adaptively performing field-structured or frame-structured coding, with a simple configuration. In a high-speed reproduction mode, a decoding process is applied to only coded image data of intra-frame coded pictures subjected to the frame-structured coding or of one field in the intra-frame coded pictures and coded image data of intra-field coded pictures subjected to the field-structured coding.

BACKGROUD OF THE INVENTION

1. Field of the Invention

This invention relates to a video decoding apparatus and method, andmore particularly, is suitably applied to a video decoding apparatus,for example, in conformity with the Joint Model of Enhanced-CompressionVideo Coding (JVT) scheme.

2. Description of the Related Art

Video processing apparatuses in conformity with a video coding schemesuch as Moving Picture Experts Group (MPEG) for efficient informationtransmission and storage have been popular for both informationproviders such as broadcast stations and information receiver such asgeneral users.

Specifically, the MPEG2 (ISO/IEC 13818-2) format is defined as ageneral-purpose video coding scheme, and now it is widely used forvarious applications for professionals and consumers because it canhandle all of an interlace scanning (interlace) format, a progressivescanning (non-interlace) format, a standard-resolution image format, anda high-resolution image format.

With this MPEG2 format, standard resolution (720×480 pixels) images ofthe interlace format and high resolution (1920×1088 pixels) images ofthe interlace format can be transmitted at bit rates of 4-8 Mbps and18-22 Mbps, respectively.

With popularization of portable terminals such as mobile telephones, acoding scheme at a much higher compression rate is demanded. To meetthis demand, an MPEG4 format was approved as a new video coding schemeas ISO/IEC 14496-2 in December 1998.

Further, for video coding for video conference, the standardization of avideo coding scheme called H. 26L (ITU-T Q6/16 VCEG) has beenprogressing. This H. 26L is known as a coding scheme providing highercoding efficiency although more operations are required for coding anddecoding, as compared with conventional coding schemes such as the MPEG2and MPEG4.

In addition, the standardization of a JVT coding scheme which is a videocoding scheme providing much higher coding efficiency have beenprogressing as well. This JVT coding scheme is realized based on the H.26L by also employing functions that the H. 26L does not have (forexample, refer to non patent reference DRAFT ISO/IEC 1/4 496-10:2002(E)).

By the way, if image data (hereinafter, referred to as JVT coded imagedata) subjected to compression and coding with the JVT coding scheme asdescribed above can be decoded by only reproducing (decoding) the imagedata of I-pictures (intra-coded picture) 1 _(I) out of I-pictures,P-pictures (inter frame predictive-coded picture) 1 _(P) and B-pictures(bidirectionaly predictive-coded picture) 1 _(B), as shown in FIG. 1, amotion compensation process which is required for the reproduction ofthe P-pictures 1 _(P) and B-pictures 1 _(B) can be omitted, therebyrealizing high-speed reproduction.

The JVT coding scheme, however, defines that a filtering process(hereinafter, referred to as a deblock filtering process) is performedon block borders of decoded pictures in order to reduce block noisespecific to a block segmentation coding format. Although the existingtechniques perform a reproduction process of only I-pictures 1 _(I),they cannot execute sufficient high-speed reproduction because thedeblock filtering process requires a large amount of operations.

As a coding mode in a case where pictures to be coded is in theinterlace format, the JVT coding scheme has a picture-based coding modewith a frame as shown in FIG. 2A or a field as shown in FIG. 2B (firstand second fields) as a coding unit and a macroblock-based coding modewith a macroblock pair 3 composed of two macroblocks 2 locating aboveand below as shown in FIG. 3 as a coding unit.

Note that, in the field-structured coding mode with a field as shown inFIG. 2B as a coding unit, the value of field_pic_flag included in aslice header of JVT coded image data is set to “1”. In theframe-structured coding mode with a frame as shown in FIG. 2A as acoding unit, the value of field_pic_flag is set to “0” and the value ofmb_adptive_frame_field_flag included in a sequence parameter set is setto “0”. In the coding mode with the macroblock pair 3 as a coding unitas shown in FIG. 3, the value of field_pic_flag of a slice header is setto “0” and the value of mb_adptive_frame_field_flag of a sequenceparameter set is set to “0”.

In addition, in the JVT coding scheme, considering that thefield-structured coding is more effective for pictures of the interlaceformat having a large amount of motion, than the frame-structuredcoding, the frame-structured coding and the field-structured coding areadaptively changed picture by picture when pictures to be coded are inthe interlace format.

Further, when the field structure is applied as a coding unit in a casewhere pictures to be coded are in the interlace format, the JVT codingscheme allows the first filed of an I-picture 1 _(I) to be coded withinthis filed (hereinafter, referred to as intra-field coding) (I-field)and the second field to be coded by reference to past field pictures(P-field) as shown in FIG. 4.

Therefore, to decode I-pictures 1 _(I) of which the first and secondfields has been coded as an I-field and a P-field, respectively,corresponding reference pictures have to be decoded in advance fordecoding the second field (P-field).

For this case, in the JVT coding scheme, a multiple reference framefunction is supported to use more than two frame pictures before andafter a target frame picture as reference pictures for the motioncompensation process at the time of coding as shown in FIG. 5.

Therefore, as shown in FIG. 6, to decode the I-picture of which thesecond field is a P-field, if the P-field uses field pictures ofP-pictures 1 _(P) and B-pictures 1 _(B) other than the I-picture asreference pictures, the P-pictures 1 _(P) and B-pictures 1 _(B) shouldbe decoded.

In short, in the JVT coding scheme, in a case where pictures to be codedare in the interlace format, the reproduction process of only I-pictures1 _(I) may not create decoded video, so that this scheme has a problemthat high-speed reproduction by reproduction of only I-pictures 1 _(I)can not be realized.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of this invention is to provide avideo decoding apparatus and method capable of performing high-speedreproduction with a simple configuration.

The foregoing object and other objects of the invention have beenachieved by the provision of a video decoding apparatus comprising adecoding means for performing a decoding process on coded image data anda control means for controlling the decoding means. The control meanscontrols the decoding means so as to decode only coded image data ofintra-frame coded pictures subjected to frame-structured coding or ofone filed of the intra-frame coded pictures and coded image data ofintra-field coded pictures subjected to field-structured coding.

As a result, this video decoding apparatus is able to sequentiallydecode only intra-frame coded pictures and intra-field coded pictureswithout performing a complicated motion compensation process.

Further, in this invention, with a video decoding method, in ahigh-speed reproduction mode, a decoding process is performed on onlycoded image data of intra-frame coded pictures subjected toframe-structured coding or of one field of the intra-frame codedpictures and coded image data of intra-field coded pictures subjected tofield-structured coding.

As a result, with this video decoding method, only intra-frame codedpictures and intra-field coded pictures can be sequentially decodedwithout performing a complicated motion compensation process.

The nature, principle and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts aredesignated by like reference numerals or characters.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a conceptual view of arrangement of types of pictures codedwith a JVT coding scheme;

FIGS. 2A and 2B are conceptual views explaining a picture-based codingmode;

FIG. 3 is a conceptual view explaining a macroblock-based coding mode;

FIG. 4 is a conceptual view explaining coding of pictures of aninterlace format;

FIG. 5 is a conceptual view explaining a multiple reference framefunction;

FIG. 6 is a conceptual view explaining reference pictures in themultiple reference frame function;

FIGS. 7A, 7B and 9 are conceptual views explaining a deblock filteringprocess;

FIG. 8 is a flowchart showing a procedure for Bs determination;

FIG. 10 is a table showing relationships between average values ofquantization parameters and threshold values;

FIG. 11 is a table showing relationships among average values ofquantization parameters, filtering strengths, and clipping values.

FIG. 12 is a block diagram showing a construction of a decodingapparatus according to this embodiment; and

FIGS. 13A to 13C are conceptual views explaining a process by afiled/frame conversion unit.

DETAILED DESCRIPTION OF THE EMBODIMENT

Preferred embodiments of this invention will be described with referenceto the accompanying drawings:

(1) Deblock Filtering Process

First the above-described deblock filtering process employed in theabove-described JVT coding scheme will be described.

The deblock filtering process is a filtering process which appliesfiltering to each boarder (hereinafter, referred to as block boarder) ofneighboring 4×4 blocks in a decoded picture in order to reduce blocknoise specific to the block segmentation coding format. In the JVTcoding scheme, a decoded picture is used as not only an output picturebut also a reference picture for successive frames, so that the deblockfiltering process of decoded pictures creates smooth reference pictureswithout block noise, resulting in improving coding efficiency andpicture quality.

With defining strength of filtering to be applied to a block boarder asBoundary Strength (hereinafter, referred to as filtering strength Bs),the deblock filtering process applies filtering to each block boarderwith the most appropriate strength. The value of the filtering strengthBs is referred to determine whether to apply the deblock filtering to ablock boarder and to define the maximum value of picture value variationafter the deblock filtering.

The maximum pixels to be corrected by filtering at each block boarderare four pixels: two pixels neighboring the boarder and pixels next tothe two pixels. With the value of filtering strength Bs and thesmoothness of the pixels as threshold values, it is determined whichpixels out of four pixels are corrected by filtering. Basically, in acase where neighboring pixels have little differences (in a case ofsmoothness or no edge), the values of the four pixels are corrected byfiltering.

In this case, all four pixels to be corrected are not directly subjectedto the filtering process. A difference value from an original pixelvalue is calculated and added. Specifically, a same absolute value isadded to two pixels neighboring a block boarder. The maximum value ofthe difference absolute value is found from a prescribed table based onthe values of a quantization parameter QP and filtering strength Bs. Alarger difference value is allowed as the quantization parameter QP andthe filtering strength Bs are larger.

In a case where the value of filtering strength Bs is 4, that is, ablock boarder is a boarder between macroblocks (hereinafter, referred toas a macroblock boarder) and at least one 4×4 block is an intra block,stronger five tap filtering is applied because the block boarder mayappear remarkably.

The deblock filtering process of this case is a process with conditionsfor decoded pictures and is performed macroblock by macroblock.Specifically, as shown in FIGS. 7A and 7B, horizontal filtering isapplied to three vertical boarders 11 ₁ to 11 ₃ in a macroblock 10 of16×16 pixels, vertical filtering is next applied to three horizontalboarders 12 ₁, to 12 ₃, and then the filtering process is applied to theleft and top macroblock boarders 11 ₀ and 12 ₀ of the macroblock 10. Thefiltering process is not applied to the edges of a picture.

At this time, filtering strength Bs to be applied to each block boarderof neighboring 4×4 blocks 13 is determined based on a procedure RT1 forBs determination as shown in FIG. 8. Specifically, it is determinedwhether one of two 4×4 blocks 13 having a target block boardertherebetween is an intra block (step SP1). When an affirmative result isobtained, it is determined whether the block boarder between the two 4×4blocks 13 is a macroblock boarder (step SP2). When this boarder is amacroblock boarder, the filtering strength Bs is determined as “4” (stepSP3). When this boarder is not a macroblock boarder, the filteringstrength Bs is determined as “3” (step SP4).

When both of the neighboring two 4×4 blocks 13 having the target blockboarder therebetween are not intra blocks, it is determined whether oneof the 4×4 blocks 13 has an orthogonal transform coefficient (step SP5).When an affirmative result is obtained, the filtering strength Bs isdetermined as “2” (step SP6).

When both of the 4×4 blocks 13 do not have an orthogonal transformcoefficient, it is determined whether reference pictures for the two 4×4blocks 13 are the same, whether the absolute difference value(|V(p,x)−V(q,x)|) of the components in a x-direction (V(p,x), V(q,x)) ofthe motion vectors of the two 4×4 blocks 13 (for example, block p andblock q) has one or more pixels, or whether the absolute differencevalue (|V(p,y)−V(q,y)|) of the components in a y-direction (V(p,y),V(q,y) of the motion vectors of the two 4×4 blocks 13 has one or morepixels (step SP7).

When any of the three conditions is satisfied, the filtering strength Bsis determined as “1” (step SP8). When none of the conditions aresatisfied, the filtering strength Bs is determined as “0” (step SP9).

Note that as filtering strength Bs to be applied to each block boarderin the macroblock 14 of a color difference signal shown by dotted linesin FIGS. 7A and 7B, a value determined for the filtering strength Bs ofthe corresponding block boarder in the mackroblock 10 of a correspondingluminance signal is used.

FIG. 9 shows a block boarder between 4×4 blocks 13 and surrounding eightpixels p₀ to p₃, q₀ to q₃ to be used for filtering. Although FIG. 9shows a case of the horizontal filtering, the vertical filtering is thesame. The pixels neighboring the block boarder 15 are p₀ and q₀, and themaximum pixels to be corrected by the deblock filtering process are fourpixels p₁, p₀, q₀, q₁. The deblock filtering process is executed onlywhen the filtering strength Bs is not “0” and the following expression(1) is satisfied.|p ₀ −q ₀|<α and |p ₁ −p ₀|<β and |q ₁ −q ₀|<β  (1)

-   -   α and β in this expression (1) are threshold values which depend        on the value of a quantization parameter QP as shown in FIG. 10.        As this quantization parameter QP is larger, α and β are loosen.        Specifically, α is a threshold value corresponding to a        variation of the values of pixels neighboring a block boarder. β        is a threshold value corresponding to a variation of the values        of pixels in each 4×4 block 13. In other words, the        expression (1) means that a region having a small variation of        pixel values is subjected to the deblock filtering process and a        region having a large variation of pixel values is identified as        an edge and is not subjected to the deblock filtering process.

In a case where neighboring 4×4 blocks 13 have different quantizationparameters QP, their average QPav is referred.

When the expression (1) is satisfied, on the other hand, the deblockfiltering process is applied to the pixel p₀ and the pixel q₀ so thatthe following expressions are satisfied:Δ=clip3(−C, (((q ₀ −p ₀<<2+(p ₁ −q ₁)+4)>>3))  (2)P ₀=clip1 (p ₀+Δ)  (3)Q ₀=clip1 (q ₀−ΔA)  (4)where P₀ and Q₀ are the pixel values of the pixels p₀ and q₀ after thedeblock filtering process.

Clip1 in the expressions (3) and (4) means [0, 255] clipping. That is,the expressions (2) to (4) mean a filtering process to add/subtract thesame value Δ to the pixel p₀/from the pixel q₀ neighboring the blockboarder 15 (FIG. 9).

Clip3 means [−C, +C] clipping. The value A is a valueincreasing/decreasing the pixel p₀/the pixel q₀ with the clipping values−C, C as the minimum and maximum values. The clipping value C of thiscase is determined based on the above-described average value QPav ofquantization parameters QP and filtering strength Bs.

Now the determination on whether to perform the filtering process on thepixels p₁ and q₁ which face to each other via the pixels p₀ and p₀, andits process will be described. This filtering process is not applied tocolor difference components. That is, only the values of pixelsneighboring a border can be corrected for color difference.

The filtering process of the pixel p₁ is executed when an activityparameter a_(P) of the 4×4 block 13 satisfies the following expression(5).a _(P) =|p ₂ −p ₀|<β  (5)

In actual, when this expression (5) is satisfied because the activityparameter a_(P) is less than the threshold value β, the filteringprocess defined by the following expression (6) is performed on thepixel p₁.P ₁ =p ₁+clip3 (−C ₀ , C ₀, (p ₂ +p ₀ +q ₀)>>1−2×p ₁)>>1  (6)As in the case of the pixels p₀ and q₀, in this filtering process, thedifference value clipped at clipping values −C₀, C₀ is added to theoriginal pixel value.

Similarly, the filtering process of the pixel q₁ is performed when theactivity parameter a_(q) of the 4×4 block 13 satisfies the followingexpression (7).a _(q) =|q ₂ −q ₀|<β  (7)At this time, the filtering process defined by the following expression(8) is performed on the pixel q₁.Q ₁ =q ₁+clip3 (−C ₀ , C ₀, (q ₂+(p ₀ −q ₀)>>1−2×q ₁)>>1)  (8)

The clipping value C₀ is defined as shown in FIG. 11 and depends on theabove-described average value QPav of quantization parameters QP andfiltering strength Bs. In short, as the quantization parameter QP andthe filtering strength Bs are both larger, a variation of pixel valueslarger than that of the original values is allowed.

The clipping value C in the expression (2) is a value obtained by adding“1” to the clipping value C₀ every time when the filtering process shownin the expression (8) is performed. Therefore, when the expressions (5)and (6) are both satisfied, C=C₀+2.

When Bs=4 (a block boarder is a macroblock boarder and one of two facingblocks having the block boarder therebetween is an intra block) anda_(p)<β (activity parameter a_(p) is less than the threshold value β), astrong filtering process defined by the following expressions (9) and(10) is applied since block noise appears remarkably in this blockboarder.P ₀=(p ₂+2×p ₁+2×p ₀+2×q ₀ +q ₁+4)>>3  (9)P ₁=(p ₃+2×p ₂+2×p ₁+2×p ₀ +q ₀+4)>>3  (10)

In addition, on luminance components, the filtering process defined bythe following expression (11) which treats one more pixel is performed.P ₂=(2×p ₃+3×p ₂ +p ₁ +p ₀ +q ₀+4)>>3  (11)

If a_(P)<β is not satisfied, the filtering process defined by thefollowing expression (12) is performed on the pixels p₀ and q₀neighboring the block border 15 (FIG. 9).P ₀=(2×p ₁ +p ₀ +q ₁+2)>>2  (12)

On the pixels q₁ to q₃ of the 4×4 block 13 (FIG. 7A) existing on theright side of the block boarder 15, the similar process is performed.

When a_(p)<β is satisfied, on the contrary, the filtering processdefined by the following expressions (13) and (14) is applied.Q ₀=(p ₁+2×p ₀+2×q ₀+2×q ₁ +q ₂+4)>>3  (13)Q ₁=(p ₀+2×p ₀+2×q ₁+2×q ₂ +q ₃+4)>>3  (14)

In addition, on the luminance components, the filtering process definedby the following expression (15) is applied.Q ₂=(2×p ₃+3×q ₂ +q ₁ +q ₀ +p ₀+4)>>3  (15)

When a_(q)<β is not satisfied, the filtering process defined by thefollowing expression (16) is applied.Q ₀=(2×q ₁ +q ₀ +p ₁+2)>>2  (16)(2) Construction of Decoding Apparatus of this Embodiment

Referring to FIG. 12, reference numeral 20 shows a decoding apparatus inconformity with the JVT coding scheme according to this embodiment. Thisdecoding apparatus sequentially stores in a storage buffer 21 image data(hereinafter, referred to as JVT coded image data) D1 given from theoutside, which has been subjected to compression and coding based on theJVT coding scheme.

The JVT coded image data D1 being stored in the storage buffer 21 isread by a skip unit 22. Under the control of a high-speed reproductioncontrol unit 23, this skip unit 22 sequentially reads all JVT codedimage data D1 from the storage buffer 21 and sends them to an inversedecoding unit 25 as read JVT coded image data D2 in a case where a userselects a normal reproduction mode as a reproduction mode with an inputunit 24.

The inverse decoding unit 25 applies a prescribed variable lengthdecoding process and arithmetic decoding process according to the formatof the received read JVT coded image data D2 to the data D2, and sendsthus obtained quantized transform coefficient to a dequantization unit26 as quantized transform coefficient data D3.

When a picture to be decoded is an intra-coded picture (I-picture orI-field), the inverse decoding unit 25 also decodes intra predictionmode information D4 being stored in the header part of the read JVTcoded image data D2 of the picture and sends the resultant to an intraprediction unit 27. When a picture to be decoded is an inter-codedpicture (P-picture, B-picture, P-field or B-field), on the other hand,the inverse decoding unit 25 also decodes motion vector information D5being stored in the header part of the read JVT coded image data D2 ofthe picture and sends the resultant to a motion prediction/compensationunit 28.

The dequantization unit 26 applies a prescribed dequantization processto the received quantized transform coefficient data D3, and sends theobtained transform coefficient which has been subjected to orthogonaltransform processes such as discrete cosine transform and Karhunen-Loevetransform, to an inverse orthogonal transform unit 29 as transformcoefficient data D6. The inverse orthogonal transform unit 29 applies aprescribed four-dimensional inverse orthogonal transform process to thereceived transform coefficient data D6 and sends the obtained differenceimage data D7 to an adder 30.

When the picture to be decoded is an intra-coded picture, the adder 30receives image data (hereinafter, referred to as predicted image data)D8 of predicted pictures which is created by the intra prediction unit27 as described later. In this case, the adder 30 sequentially adds thedifference image data D7 from the inverse orthogonal transform unit 29and the predicted image data D8 from the intra prediction unit 27, andsends the obtained decoded image data of the I-picture or I-field to adeblock filtering unit 31 as decoded image data D10.

When the picture to be decoded is an inter-coded picture, the adder 30receives image data (hereinafter, referred to as reference image data)D8 of a reference picture which is created by the motionprediction/compensation unit 28 as described later. In this case, theadder 30 sequentially adds the difference image data D7 from the inverseorthogonal transform unit 29 and the reference image data D9 from themotion prediction/compensation unit 28, and sends the obtained decodedimage data of P-picture, B-picture, P-field or B-field to the deblockfiltering unit 31 as decoded image data D10.

In the normal reproduction mode, under the control of the high-speedreproduction control unit 23, the deblock filtering unit 31 sequentiallyapplies the above-described deblock filtering process to the receiveddecoded image data D10 and stores the obtained image data of decodedpictures in which block distortion has been eliminated, in a framememory 32 as filtered decoded image data D11.

The filtered decoded image data D11 being stored in the frame memory 32is read out frame-by-frame or field-by-field after being rearranged inan order before the JVT coding is performed by means of an picturerearrangement buffer 33. Then in the normal reproduction mode, the datais converted to an analog signal in a digital-to-analog converter 34 andis output to the outside as a reproduction video signal S1 under thecontrol of the high-speed reproduction control unit 23.

When the intra-prediction unit 27 receives intra-prediction modeinformation D4 from the inverse decoding unit 25, it creates image dataof a predicted picture of an intra-coded picture to be decoded, based onthe intra-prediction mode information D4 and the filtered decoded imagedata D11 being stored in the frame memory 32, and sends this data to theadder 30 as predicted image data D8 as described above.

When the motion prediction/compensation unit 28 receives the motionvector information D5 from the inverse decoding unit 25, it createsimage data of a reference picture based on the motion vector informationD5 and the filtered decoded image data D11 being stored in the framememory 32, and sends this data to the adder 30 as reference image dataD9 as described above.

Then the filtered decoded image data D11 being stored in the framememory 32 is read frame-by-frame or field-by-field after beingrearranged in an order of pictures before the JVT coding is performed bythe picture rearrangement buffer 33. In the normal reproduction mode,under the control of the high-speed reproduction control unit 23, thedata is converted into an analog signal in the digital-to-analogconverter 34 and is output to the outside as a reproduction video signalS1.

As described above, the decoding apparatus 20 performs normalreproduction on received JVT coded image data D1 in a normalreproduction mode.

In the case where the user selects a high-speed reproduction mode as areproduction mode with the input unit 24, on the other hand, thedecoding apparatus 20 deletes JVT coded image data D1 of coded pictures(P-picture, B-picture, P-field and B-field) other than JVT coded imagedata D1 of I-frame (I-picture) subjected to the frame-structured codingand JVT coded image data D1 of I-field subjected to the field-structuredcoding, out of the JVT coded image data D1 being stored in the storagebuffer 21, from the storage buffer 21 under the control of thehigh-speed reproduction control unit 23.

Specifically, since the value of field_pic_flag included in the sliceheader of the JVT coded image data D1 of a picture subjected to theframe-structured coding is “0” and the value of field_pic_flag in theJVT coded image data D1 of a picture subjected to the field-structuredcoding is “1” as described above, the skip unit 22 deletes from thestorage buffer 21 JVT coded image data D1 other than the JVT coded imagedata D1 of I-picture for pictures with the field_pic_flag of “0” and theJVT coded image data D1 of I-field for pictures with the field_pic_flagof The skip unit 22 sequentially reads the remaining JVT coded imagedata D1 of I-picture having the frame structure and the remaining JVTcoded image data D1 of I-field having the field structure, from thestorage buffer 21, and sends them to the inverse decoding unit 25 asread JVT coded image data D2.

As a result, the read JVT coded image data D2 is processed by theinverse decoding unit 25, dequantization unit 26, inverse orthogonaltransform unit 29, and adder 30 as in the case of the above-describednormal reproduction mode. Thus obtained decoded image data D10 ofI-picture or I-field is given to the deblock filtering unit 31.

Under the control of the high-speed reproduction control unit 23, thedeblock filtering unit 31 stores the received decoded image data D10 inthe frame memory 32 as filtered decoded image data D11 as it is, withoutperforming the deblock filtering process.

The filtered decoded image data D11 being stored in the frame memory 32is used for creation of the intra-predicted image data D8 or referenceimage data D9 in the intra prediction unit 27 and the motionprediction/compensation unit 28 as described above, and is also readfrom the frame memory 32 at prescribed timing and stored in the picturerearrangement buffer 33.

In addition, in the high-speed reproduction mode, under the control ofthe high-speed reproduction control unit 23, the filtered decoded imagedata D11 being stored in the picture rearrangement buffer 33 isrearranged by the field/frame conversion unit 35 in an order of picturesbefore the JVT coding is performed and is read frame-by-frame orfield-by-field.

Then in the high-speed reproduction mode, under the control of thehigh-speed reproduction control unit 23, when the filtered decoded imagedata D11 read from the picture rearrangement buffer 33 is data ofI-picture having the frame structure as shown in FIG. 13A, thefield/frame conversion unit 35 deletes the filtered decoded image dataD11 in the second field as shown in FIG. 13B, creates image data bycopying the filtered decoded image data D11 of a line one above in thefirst field as filtered decoded image data D11 of the corresponding linein the second field as shown in FIG. 13C, and sends the image data tothe digital/analog converter 34 as field/frame conversion image dataD12. As a result, in the high-speed reproduction mode, under the controlof the high-speed reproduction control unit 23, this field/frameconversion image data D12 is converted into an analog signal in thedigital-to-analog converter 34 and is output to the outside as areproduction video signal S1.

On the contrary, in the high-speed reproduction mode, when the filtereddecoded image data D11 read from the picture rearrangement buffer 33 isdata of I-field having the field structure as shown in FIG. 13B, thefield/frame conversion unit 35 creates image data by copying thefiltered decoded image data D11 of a line one above in the first fieldas filtered decoded image data D11 of the corresponding line in thesecond field, and sends this image data to the digital-to-analogconverter 34 as field/frame conversion image data D12. As a result, inthe high-speed reproduction mode, under the control of the high-speedreproduction control unit 23, this field/frame conversion image data D12is converted into an analog signal in the digital-to-analog converter 34and is output to the outside as a reproduction video signal S1.

As described above, in a case where the high-speed reproduction mode isselected, the decoding apparatus 20 performs high speed reproduction ofreceived JVT coded image data D1 by decoding only I-pictures forpictures subjected to the frame-structured coding or only I-fields forpictures subjected to the field-structured coding.

(3) Operation and Effects of this Embodiment

According to the above configuration, in the high-speed reproductionmode, as to pictures of the interlace format, the decoding apparatus 20decodes only I-pictures for pictures subjected to the frame-structuredcoding and only I-fields for pictures subjected to the field-structuredcoding, without performing the deblock filtering process.

Therefore, in the high-speed reproduction mode, the decoding apparatus20 does not need complicated processes such as a motion compensationprocess which is required for decoding P-pictures, B-pictures, P-fieldsor B-fields, and is able to eliminate time required for the deblockfiltering process, resulting in performing high-speed reproduction ofJVT coded image data D1 with a simple consfiguration.

Further, in this case, when the decoding apparatus 20 decodes onlyI-fields (first field) of I-pictures subjected to the field-structuredcoding, it creates reproduction video of the I-pictures by copying themin the second field. When the decoding apparatus 20 decodes I-picturessubjected to the frame-structured coding, it creates reproduction videoof the I-pictures by copying the first field in the second field. As aresult, I-pictures subjected to the frame-structured coding andI-pictures subjected to the field-structured coding can have the samepicture quality.

Thus the decoding apparatus 20 is able to previously and effectivelyprevent distortion of video reproduced at a high speed due to such asituation that decoded pictures of I-pictures subjected to theframe-structured coding having good picture quality and decoded picturesof I-pictures subjected to the field-structured coding having badpicture quality are mixed and displayed.

In a case of creating reproduction video by copying the first field inthe second field to reproduce pictures of I-picture or I-field asdescribed above, although the resolution in a vertical directiondeteriorates by half, this deterioration does not cause any problembecause human beings cannot recognize it in the high-speed reproduction.

According to the above configuration, in the high-speed reproductionmode, as to pictures of the interlace format, only I-pictures forpictures subjected to the frame-structured coding and only I-fields forpictures subjected to the field-structured coding are decoded, withoutapplying the deblock filtering process. Therefore, complicated processessuch as the motion compensation process is not required and timerequired for the deblock filtering process can be omitted, thus makingit possible to realize a decoding apparatus capable of performinghigh-speed reproduction of JVT coded image data D1 with a simpleconfiguration.

(4) Other Embodiments

In the embodiment described above, this invention is applied to adecoding apparatus 20 in conformity with the JVT coding scheme. Thisinvention, however, is not limited to this and can be widely applied toother decoding apparatuses which decode coded image data composed ofimage data coded with a prescribed coding scheme for adaptivelyperforming field-structured or frame-structured coding.

In this case, in the embodiment described above, the skip unit 22,inverse decoding unit 25, dequantization unit 26, inverse orthogonaltransform unit 29, adder 30, intra prediction unit 27, and motionprediction/compensation unit 28 composes a decoding means for decodingcoded image data (JVT coded image data D1). However, the decoding meanscan have a construction appropriate for a coding scheme that a decodingapparatus employing this invention is in conformity with.

Further, in this case, in the embodiment described above, since thecoded image data to be decoded has been coded with the JVT codingscheme, a filtering means for performing a filtering process on decodedimage data performs the deblock filtering process. This invention,however, is not limited to this and if this invention is applied to adecoding apparatus for decoding image data coded with another codingscheme and the filtering process of the decoded image data requires alarge amount of operations and takes a lot of time, the filtering meanscan be controlled so as not to perform the filtering process in thehigh-speed reproduction mode as in the case of the embodiment describedabove.

Further, in the embodiment described above, the decoding means composedof the skip unit 22, inverse decoding unit 25, dequantization unit 26,inverse orthogonal transform unit 29, adder 30, intra prediction unit 27and motion/compensation unit 28 decodes only I-pictures having the framestructure and I-fields having the field structure, out of the JV codedimage data D1 being stored in the storage buffer 21, under the controlof the high-speed reproduction control unit 23 serving as a controlmeans for controlling the decoding means. This invention, however, isnot limited to this and only one of the first and second fields of theI-pictures can be decoded, instead of the I-pictures having the framestructure. In this case, the skip unit 22 may delete the JVT coded imagedata D1 of one field of the I-pictures together with JVT coded imagedata D1 of P-pictures etc., from the storage buffer 21.

In addition, in this case, the field/frame conversion unit 35 serving asa field/frame conversion means for creating the image data of framepictures from the image data of field pictures may create the image dataof decoded pictures by taking the filtered decoded image data D11 of thefirst or second field obtained by decoding I-pictures having the framestructure as one field and copying the filtered decoded image data D11in the other field.

According to this invention described above, the video decodingapparatus for decoding coded image data composed of image data subjectedto coding with a prescribed coding scheme for adaptively performingfield-structured or frame-structured coding comprises a decoding meansfor performing a decoding process on coded image data and a controlmeans for controlling the decoding means. The control means controls thedecoding means so as to perform the decoding process on only coded imagedata of intra-frame coded pictures subjected to the frame-structuredcoding or of one field in the intra-frame coded pictures, and codedimage data of intra-field coded pictures subjected to thefield-structured coding. Therefore, only intra-frame coded pictures andintra-field coded pictures can be sequentially decoded, withoutperforming a complicated motion compensation process, thus making itpossible to realize a video decoding apparatus capable of performinghigh-speed reproduction with a simple configuration.

In addition, according to this embodiment, with a video decoding methodfor decoding coded image data composed of image data subjected to codingwith a prescribed coding scheme for adaptively performingfield-structured or frame-structured coding, in the high-speedreproduction mode, only coded image data of intra-frame coded picturessubjected to the frame-structured coding or of one field of theintra-frame coded pictures and coded image data of intra-field codedpictures subjected to the field-structured coding are decoded.Therefore, only the intra-frame coded pictures and intra-field codedpictures can be sequentially decoded, without performing a complicatedmotion compensation process, thus making it possible to realize a videodecoding method capable of performing high-speed reproduction with asimple configuration.

While there has been described in connection with the preferredembodiments of the invention, it will be obvious to those skilled in theart that various changed and modifications may be aimed, therefore, tocover in the appended claims all such changes and modifications as fallwithin the true spirit ad scope of the invention.

1. A video decoding apparatus for performing a decoding process on codedimage data comprising image data subjected to coding with a prescribedcoding scheme for adaptively performing field-structured coding orframe-structured coding, the video decoding apparatus comprising:decoding means for performing the decoding process on the coded imagedata; and control means for controlling the decoding means, wherein thecontrol means controls, in a high-speed reproduction mode, the decodingmeans so as to perform the decoding process on only the coded image dataof intra-frame coded pictures subjected to the frame-structured codingor of one field in the intra-frame coded pictures and the coded imagedata of intra-field pictures subjected to the field-structured coding.2. The video decoding apparatus according to claim 1, further comprisingfiltering means for performing a prescribed filtering process on decodedimage data obtained by performing the decoding process on the codedimage data, wherein the control means controls, in the high-speedreproduction mode, the filtering means so as not to perform thefiltering process on the decoded image data.
 3. The video decodingapparatus according to claim 2, wherein the filtering process is adeblock filtering process to reduce block noise.
 4. The video decodingapparatus according to claim 1, further comprising field/frameconversion means for taking as one field decoded image data obtained byperforming the decoding process on the coded image data, and creatingimage data of a decoded picture by copying the decoded image data in theother filed.
 5. A video decoding method for performing a decodingprocess on coded image data comprising image data subjected to codingwith a prescribed coding scheme for adaptively performingfield-structured coding or frame-structured coding, the video decodingmethod comprising, in a high-speed reproduction mode, performing thedecoding process on only the coded image data of intra-frame codedpictures subjected to the frame-structured coding or of one field in theintra-frame coded pictures and the coded image data of intra-field codedpictures subjected to the field-structured coding.
 6. The video decodingmethod according to claim 5, wherein a prescribed filtering process isapplied to decoded image data obtained by performing the decodingprocess on the coded image data in a normal-speed reproduction mode, andthe filtering process is not performed on the decoded image data in thehigh-speed reproduction mode.
 7. The video decoding method according toclaim 6, wherein the filtering process is a deblock filtering process toreduce block noise.
 8. The video decoding method according to claim 5,wherein image data of decoded pictures is created by taking as a firstfield decoded image data obtained by performing the decoding process onthe coded image data and copying the decoded image data in a secondfield.